Telephone system



Jan. 16, 1945 H. w.` BALZER TELEPHONE SYSTEMv Filed Dec. 17, 1942 l0 Sheets-Sheet 1 ATTORNEYS H. W. BALZER TELEPHONE SYSTEM Filed Dec. 17, 1942 l0 Sheets-Sheet 2 Jan. 16, 1945.

Jan. 16, 1945. H, w. BALZER TELEPHONE SYSTEM Y Filed Dec. 17, 1942 l0 Sheets-Sheet I5 Il f w m m .|I|I|H||l |||||l|... f NNm Q M .IIII H H MB vnlv omzz. Nvo om "II H I 25 mw. .m .32 r ,18m NM mz; mm .55 x2: 5oz: @88,228 m am H o.. 03, o.. m ||I|||| /Im gz: 53 wm 555mm :om V 0% yf w25: .3E oomz ESE \o INH oa @2582. 8 I do mmf com, :35o 552mm m wz: d8 24.28.,: -Jem J l E Se hm@ @om mzxm ESQ@ O mOEn .ZmO

@mmm mm o2 25 mz: mmf-Hummm .joh do QOL 53 Jan. 16, 1945.

Filed Dec. 1'7, 1942 H. W. BALZER TELEPHONE SYSTEM l0 Sheets-Sheet 4 4oon 40o@ 400.@

33 4H 4|2 TOLL REPT.' REPT. LINE 33| 332 l 4|5 g 4B 4m CENTRAL OFFICE IO DISTANT EXCHANGE 30o..

FIG. Il

FIG. I F|G.2

FIG.3

FIG -12 u Frs. FIG. FIG. FIG. HG. FIG. FIG.

4 5 s A7 s e lo INVENTOR. HARVEY W. BALZER Jan. 16, 1945- H- w, BALZER I 2,367,635

TELEPHONE SYSTEM Filed DBC.A 17, 1942 l0 Sheets-Sheet 5 'l 57| C502 59113W 595 l TOLL LlNE CIR. '500 suPY. LAVE V 5u' K fd v u 574 W EQ2 coNT r 56| fbi,

552AJ E592 I 593 5 83 lfsla l sesf. W \5|3' 515 -oql.

INVENTOR. F 5 HARvEv w. BALzER ATTORNEYS Jan. 16, 1945. H. w. BALZER 2,367,635

TELEPHONE SYSTEM Filed Dec. 17, 1942 10 Sheets-Sheet 6 693 PULS POLAR (vf-M R610, L624 l., \suPY. ma S'MPLEX www-+A.

4J I 50H I A INVENToR. F| 6 HARVEY w. sALzsn BY v ATTORNEYS Jan. l5, 1945.

H. w. yBALzl-:R 2,367,635

TELEPHONE SYSTEM Filed Dec. 17, 1942 1o sheets-sheet 7 L795 i/QGI glam C794: 62 n 740 GEN. 762 L y Ana 1763 \772 74| my I. 73| infn' R770- -o-Il M R760 -OT- RING. X752 IsuPY. HOLD 7|o T04. 732 R750 RING,

722 75?/ *wf-m, wf-n4 f723 USYl A 78o 79s S R720! 1 97 M53 754/f 78W a2 *-Imm flo-'Q/Y M785 Q-Il' IN VENTOR. HARVEY W BALZER ATTORNEYS Jan. 18, 1945.;

H. W. BALZER TELEPHONE SYSTEM Filed Dec. 17, 1942 l0 Sheets-Sheet 8 INCOMING sELEcToR PEG. E 3'5 310 TO-LOCAL sw TRAIN 79m Y 8I0q C`8II T E 82' TONE DETECTOR BQ@ c80II T 0808 818 A 0808 A881 I START IzoIRM. 08I8 4| M62 C804 R820 f s IRM.n 08|? A842 C8I2 70822 s874 8a3/ i- T FLASH 843/ 873 5I 08I3\ T824 CON 8 cali R830 R835 V844 TON 9876 83 836 R840 852 'Rsego 0877 8285?; 855\ lfm Y S875 d J ooo' o 7| 5 N0 873 CBO IDIGIT swITcH TONE 0ETE0TIN0 UNIT SI5 50I7 INVENTOR.

HARVEY W BALZER ATTORNEYS TELEPHONE SYSTEM Filed Dec. 1'7, 1942 l0 Sheets-Sheet Q ,Csm FIG. 9 A im 9Io3 "B330 INCOMING I Gels 94| TRUNK CIR. I \w42v 9M QLD ANS. R940 96o 932 I Y I 963ml ATTORNEYS Jan.. 16, 1945.

H. W. BALZER TELEPHONE SYSTEM Filed Dec. 17, 1942 N 1013/1 /l0l4 |033 ,065.

f 10 Sheets-Sheet l0 |327. Llgd Jloza u o-I TOLL BOARD 320 RIO70{ FSWITGH SLAVE INVENTOR. HARVEY Vl BALZER 5 MKM?, w1 #0170 AT TORNE YS Patented Jan. 16, 1945 I UNITED STATES 2,367,635 l l TELEPHONE SYSTEM O Harvey W. Balzer, Downers Grove, Ill., assignor to Automatic Electric Laboratories, Inc., a corporation of Delaware Application December 17, 1942, Serial No. 469,297

' 22 claims. (ci. 179-27) The present invention relatesto telephone systems and more particularly to toll switching systems of the character Yof that. disclosed in the copencl'dappiication of Harvey W. Balzer, Se-\ rial No. 462,543, tiled October 19, 1942, now Patent No. 2,353,212, granted July 11, 1944.

In atoll switching system of the type noted a plurality of exchanges are provided, each two exchanges beinginterconnected by a group'of two-way toll trunks. Each exchange comprises a group of toll line circuits individually terminating the toll trunks extending thereto, associated automatic switching apparatus and an operator switchboard, whereby calls may be routed over Further features of the invention pertain to the particular connection and arrangement of the circuit elements of the system, whereby the above-outlined and ladditional operating features 6 are attained.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will bestbe understood by reference to the following specification l0., taken in connection with the accompanying drawings, in which `Figs. 1 to 3, inclusive, taken together, illustrate the general arrangement of a telephone system embodying the present invention; Fig. 11 illustratesthe mode of combinthe toll trunks to and from the various operator 15 ing Figs. 1 to 3. inclusive, t0 form a unified sysparticular switching stage of an automatic switch train which encounters a busy condition during the operation thereof.

Another object of the invention is to provide in a toll switching system in conjunction with the determining arrangement noted, improved apparatus for translating the determination made into suitable supervisory signalswhich are returned over the trunk incoming to the switch train.

Another object of the invention is to provide in a telephone system a repeater arrangement between an incoming trunk and an associated switch train, which repeater arrangement embodies improved facilities for controlling supel'VSion over the trunk from the switch train.

A further object of theinvention is to provide in a telephone system comprising an incoming trunk and a switchboard including a plurality of operator positions, an' improved arrangement for selectively indicating the presence of a call to be answered on the trunk to the different operator positions at the switchboard.

tem; Figs. 4 to 10, inclusive, taken together, il-

lustrate the details of a portion of the system having incorporated therein the features ofthe invention .as briefly outlined above; and Fig. v12

illustrates the mode of combining Figs. 4 to 10,

inclusive, to form ,the portion of the system.

Description of the apparatus incorporated in the system Referring now more particularly to Figs." 1 to 3, inclusive, of the drawings, the telephone system there illustrated comprises a central oilice I0 of the fully automatic type, a remote toll oiiice No. 1, a remote toll oflice No. 2, a remote manual oilice No. 1 provided with a switchboard Il, a

remote manual oilice No. 2 provided with a switchboard 42, a remote automaticexchange 3,

` and a distant exchange 300. The central oilice I0 is illustrated as serving a plurality of substations A, B, C, etc., which are connected with the automatic switching equipment of the ofllce by.

exchange 300 serving amumber of substations, in-

cluding the substation X. It is lnoted in this regard that the two toll oiilces, the central office il and the distant exchange 300 are provided with automatic switching equipment for han- A still further object of the invention is to prodling both local calls and interoice toll calls.

vide in a telephone system comprising a trunk,

digit control switching apparatus operative t0 route a call over the trunk and a switchboard including a plurality of operator positions, an improved circuit arrangementfor selectively releasing the switching apparatus in order to absorb digits transmitted thereto and for selectively indicating the presence of a call to 4be answered on the trunk to the diiierent operator positions at the switchboard.

The four oiiices and the two exchanges remote from the central oiiice Il are trunk or toll `line connected with the central oilice I0 by means of a number of toll trunks which are utilized exclusively in the handling of toll trame. Thus,

and 333 lwhich respectively terminate in the trunk or toll line circuits 21, 28, 29, 4 and 44| are provided for connecting the three other outlying ofiices and the two remote exchanges with the central o'lce I0. It will be understood in this regard that the number of toll trunks provided to connect the central oiilce I with any one of the four outlying oflices and any one of the two remote exchanges is determined by the amount of toll traffic therebetween. For example, if the two illustrated toll ofllces are geographically situated to handle a large volume of toll traiiic involving the central office III, two tor more. groups of trunks, each including as many as ten trunks, may be required therebetween.

The trunks utilized to connect the central ofce I0 with the manual oilice No. 1 are of the ring-down type; while the trunks utilized to connect the central office I0 with the manual ofilce No. 2 are of the combination dial and ring-down type. Accordingly, the trunk circuits 28 and 29 are, respectively, of the well-known ring-down and combination dial and ring-down types and are used to terminate these trunks in the central ofiice IIL The trunk circuit 4 which terminates the one-way trunk 2 in the central oflice I0 is of the automatic-to-automatic type, being provided with facilities for repeating received dial impulses to the trunk 2 on lan outgoing call to the' exchange 3. The trunks utilized to connect the central oice I0 with the-two toll oflices and with the distant exchange 300 are of the toll dial type. Accordingly, the trunk circuits 26, 21, and 400 may be substantially identical and are of the vtoll dial type. A

The automatic switching equipment provided in the central oiilce I0 is of two different types requiring two corresponding different forms of directive control. More specifically, the local automatic switching equipment comprising the switch trains 3|, 33 and 4I includes selector and connector switches requiring the well-known revertive type of directive control. This form of directive control is commonly used in the twomotion selector and connector switches of the rotary-'vertical type conventionally employed in.

auto-manual systems. 'I'he toll switching equipment provided in the central office I0 is of the well-known Strowger type employing straightforward impulsing or directive control in the setting of the selected switches of a train. Accordingly, provisions are made at certain switching stages of the toll switching equipment for converting straightforward .directive control into revertive control for the purpose of permitting the toll operators to obtain access to the subsi-.ations served by the central office I0.

In general, the facilities for handling toll calls in the central oftlce I0 and each of the two illustrated toll oillces may be identical. It will be understood, therefore, that the following description relative to the toll switching equipment provided in the central 'oflice III may be considered as applying also to the toll switching equipment provided in the toll` office No. 1 and the toll ofce No. 2. This equipment provided in the central oflice I0 includes an -position toll operator switchboard II which is capable of" handling toll calls of all types. It is contemplated that each position of this switchboard will function as a universal position, whereby both C. L. R. or outward toll calls requiring ticketing and inward toll calls requiring no ticketing may be handled at any operator position thereat. Facilities are also provided in commotion with each of the eight operator positions for permitting the operatorto initiate delayed calls in the handling of point-to-point trafllc. The trunking plan of the system also contemplates that all interposition or T.l X calls shall be routed to either the first position or the second position at the switchboard II. To this end, the illustrated T. X position distributor I4 is limited'in its operation to the distribution of calls to the first and second positions of the switchboard I l.

The call handling facilities provided at and in association with each of the eight positions of lthe switchboard II are identical. Briefly considered, these facilities as provided at the No. l position of the switchboard comprise an operator position circuit I8, a plurality of links, including the link I5, for routing calls to and from the position circuit I8 and a link distributor I9 for selecting idle ones of the links individual to the No. 1 position of the switchboard I I for use in a predetermined order. Each of the links provided at the switchboard II includes an answer or line finder switch and a call or selector switch, the illustrated link I5 comprising an answer switch I8 and a call switch Il. For the purpose of directing the extension of a connection from the No. 1 position from the switchboard I I either through` the front end or the rear end of a link selected by the distributor I9, impulse sending equipment is provided which comprises a key set 22, a sender control circuit 20 `and -a register sender 2|, including the impulse sender 2IA and the digit registers 2IB.

Incoming calls appearing before the various links of the switchboard II for answering are received in trunks which differ slightly in arrangement in accordance with the particular character of the cells. For example, inward toll calls originating in the tolloflice No. 1, the toll cnice No. 2 or in the distant exchange 300 may be extended to the switchboard II for answering through a group of inward trunk circuits, including the trunk circuit 25, or a groupof interposition trunk circuits, including the trunk circuit 24. Outward toll ca1ls,.on the other hand, may be extended to the switchboard il for answering through a group of C. L. R. trunk circuits, including the trunk circuit 23. In order to preselect the different positions of the switchboard II for use in a predetermined order as calls are extended to the trunk circuits appearing before the rear ends of the links provided atthe different positions of the switchboard, a position distributor I3 isprovided for the purpose of allotting inward and outward tolllcalls alternately to the switchboard II. For the additional purpose of controlling the position and link start relays of the position and link circuits provided at the different positionsof the switchboard II, a start circuit I2 common to the inward and outward trunk circuits is provided. This start circuit is also utilized in the extension of calls to the switchboard II from the ring-down trunks extending to the manual ofiice No. 1, calls on these trunks being classified in the same category as outward or C.` L. R.. calls originating in the area, served by the central oilice I0.

In the illustrated trunking plan, three selec tive or directively controlled switching stages are providedin the toll switching equipment of the central onice III. More specifically, calls incoming from the toll cnice No. l, the toll oillce No. 2, the manual olce No. 2 and the distant exchange 300 are rst handled at a primary switching stage which includes a group of nnderselector.links, one of which is indicated at l! as comprising a nder 36 and a selector 31. For the purpose of allotting these links for use in a predetermined order, a link distributor 39 is provided for these links. Callsw incoming from the indicated remote` oices and exchange may either be extended through the local automatic switching equipment comprising the switch train 3| to the substations served by the central oice I0, to the toll operator switchboard I or to other of the toll and manual oiiices and the exchanges remote from the central oiiice Ifll. In the last-mentioned case, the second switching stage, comprising the toll second se-- lector 32, or the second and third toll switching stages, comprising both the toll second selector 32l oiice before the call can be routed through this I equipment to the desired substation. To this end, a group of register senders is provided in association with the links forming the first switching stage of the toll switchingl equipment. More speciically, the illustrated register sender 40 of this group has the function) of converting received switch directing impulses into the rvertive type of switch directing signals which are required for control of the local automatic switching equi-pment in the central oiiice Ill. These senders are common to the links provided at the primary switching stage of the toll switching equipment and may be seized through register selectors individual to the links. Thus, the illustrated link 35 is shown as having associated therewith a register selector 38 through which the register sender 40 may be seized.

In the routing of calls from the toll operator switchboard Il to the remote offices and exchanges through the frontends of the links provided thereat, the primary and secondary switch-Y ing stages of the toll, switching equipment are' not required. It will be notedin this regard that a straight multiple is provided between the contact levels of the toll second selectors 32 etc. and the call switches of the links I5 etc. associated with the diierent positionsy of the switchsuch calls, however, the toll third selectors 34 etc. may be required in order to gain accessfto the desired group of interofllce trunks. For the purpose of permitting calls to be extended Depending upon the destination of ond selectors, including the selector 55, is provided; which selectors are`directly accessible to the call switches of the links I5 etc. and to the delayed call selectors 41 etc. Each of the second selectors 55 etc. is similar to the selectors 31 etc. in that provisions are made therein for transmitting received switch directing signals through an associated register selector to a register sender. More' particularly, the second selector 55 is provided with an associated registerselector 56 having accessto a register sender 51; the register sender 51 having the function of converting the received signals into the form required to control the switches of the local automatic switching equipment.

The trunking plan of the system is such that certain outward or C. L. R. toll calls which require ticketing in the central oilice I0 and which originate in the central oice area are handled at a toll switchboard 30 of the manual type. In

order to permit the operators attending the manual switchboard 30 to gain access to the trunks extending to the two toll oices, to the two manual oices, and to the distant exchange 300, this switchboard is trunk connected to the trunk circuits terminating the interoice toll trunks men- I0 and inthe toll line circuit 500 provided in the distant exchange 300. Also each of these toll trunks comprises a plurality of repeaters of the vacuum tube type; the toll trunk 333 comprising i the repeaters 33| and 332illustrated, respectively vdisposed in the central oiice I0 and in the distant exchange 300. The toll line circuit 500 isprothrough the rear ends of the links associated with the switchboard l| I, a group of delayed call selec.-

tors, including the selector 41, is provided. These delayed call selectors 41 etc. are commonly acces'- sible to all positions of the switchboard Il through the iirst level of the bank contacts ofthe answer switch of each'link I5 etc., and astraight multiple is provided between the bank contacts of the delayed call selectors l1 etc., the toll second selectors 32 etc., and the call switches of the links I5 etc.

Thus, each position of the switchboard ||is permitted to have access to the same routes over the front and rear ends of the links i provided thereat.

vided with an incoming selector 3|5 and a ltone detector 800 individual thereto in the distant exchange 300. Also the distant exchange 300 comprises toll switching equipment including not only the incoming selectors 3|5 etc. but also a group ot toll transmission selectors and a number of groups of toll connectors. The group of toll transmission selectors includes the selector 3|| which is accessible viathe trunk 3 I 0 tothe incoming selector 3|5; and one of the groups of toll connectors includes the connector 3|2 which is accessible via the trunk3|3 to the toll selector 3| It is noted that the toll connector 3|2 has access via the subscriber line 322 to the substation X illustrated.

Further the distant exchange 300 comprises local switching apparatus including a number of local links 30| etc.; the local link 30| including a local finder 302 and va local connector 303.

Also line circuits 32| etc. are individually associmatic switchingequip'ment of the central omce I0. 7

ated with the` lines 322 etc.. extendingl to the substations X etc. Further a local link distributor 304 is associated with the group of local links for the purpose of allotting idle ones of these links to the various line circuits 32| etc. Finally the distant exchange 30| comprises a toll switchboard 320 including a number of operator positions. More particularly, the toll'board 3 2'0 is of the manual type and includes` an inward position, an information position, a call order position, and ten interposition or T. X positions. .The toll switchboard 320 is 'accessiblejto' the incoming To gain access to this equipment, a group of secselector 3| 5 etc. by way of a group of incoming trunk circuits, including the trunk circuit 000. Further the toll board 320 has access to a number of trunks 50| etc. individually extending to the toll line circuits 500 etc., whereby the toll trunks 333 extending between the distant exchange 300 and the central ofilce I0 may be utilized for the purpose of extending outgoing calls from the toll board 320.

The elements of the system illustrated in Figs. 1 and 2 are either disclosed or properly identiiled in the previously mentioned copending Balzer application; the toll line circuit 000 is substantially identical to thev trunk circuits 20 and 21; the repeaters 33| and 332 are of any suitable type and the line circuits 32| etc. are of any suitable typo. Also the incoming selectors 3|5 etc. are of the conventional Strowger drop-back type; the toll transmission selectors 3|| etc. and the toll connectors 3|2 etc. are of the conventional Strowger types; the local finders 302 etc. and the local connectors 303 etc. are of the conventional Strowger type; and the local link distributor 300 is of any suitable type.

In the distant exchange 300, preferably, each of the toll line circuits is identical to the toll linef circuit 500 which comprises, as best shown in Figs. 4 to 7, inclusive, a repeating coil 0I0, agrelay group including va switch relay R5|0, three supervisory relays R500, R|0 and R110, a seizure f relay R520, a siezure slave relay R530, two rering ated with the toll line circuit 500 which comprises,

as shown in Fig. 8, a tone detecting unit 0|5 of the vacuum tube type and 'of any suitable form. Also the tone detector 000 comprises a digit switch 010 of the vminor type, includingA a single wiper 01| provided with an associated contact bank, a magnet M012 for driving the wiper noted step by step in the clockwise direction, a magnet M013 for releasing the wiper noted and for causing it to be returned to its normal rotary position, ani two sets of switch springs S010 and S015 whic i are actuated when'the wiper noted is moved away from its normal rotary position. Further the tone detector 000 comprises a relay group, including a start relay R020, a iiash relay R030, two control relays R035 and R050, a tone switch relay R000 and a tone relay R000; and a control network connected and arranged in a manner more fully described hereinafter.

Preferably, each of the incoming trunk circuits is identical to the incomingtrunk circuit 900 which comprises, as shown in Figs.- 9 and 10, a repeating coil |000 and a signal switch |030 of the minor type, including two wipers |00| and |002 provided with individually associated contact banks, a magnet M|033 for driving the wipers noted step by step in the'counterclockwise direction, a magnet M|000 for releasing the wipers noted and for causing them to be returned to their normal rotary positions, and two sets of switch springs S31| and S|005 which are actuated when the wipers noted are moved away from their normal rotary positions. Also the incoming selector 000 comprises a relay group, including a T. X relay R020, a line relay R030, a hold relay R000, a digit relay R050, an answer relay R360, a reverse battery relay R|0|0, three ring relays R|020, R|030 and R|000, a supervisory relay Rl050, a switch relay R|000 and a switch slave relay R|010; and a control network connected and arranged in a manner more fully described hereinafter.

As previously noted, the toll board 320 is of the manual type and comprises a plurality of operator positions, including the inward position |025 illustrated which is provided with a signal lamp L|055 individual thereto. Each operator position at the switchboard comprises a jack upon which an incoming call on the incoming trunk circuit 900 may be answered; the inward position |025 being provided with the jack J |025 illustrated. Also each operator position at the toll board 320 is provided with a jack and an associated signal lamp associated with the trunk 50| extending to the toll line circuit 500; the inward position |025 being provided with the jack J |020 and the signal lamp L|050 associated with the trunk 50| extending to the toll line circuit 500.

A better understanding of the connection and arrangementv of the system will be facilitated from a consideration of the detailed operation of the various pieces `of apparatus incorporated Vtherein'incident to the completion of the various calls between the central oillce |0 and the distant`exchange 300, as will appear hereinafter.

Initiation of a call :trom the central apice to the distant' exchange Considering now the initiation of a call to the distanct exchange 300 from the central office I0, it is noted that the call may be initiated in the central oflce |0 either at the toll switchboard or at the toll board 30, or the call may be Ainitiated at one of the two remote toll oiiices or at the manual oilice No. 2 and extended via the central oilice I0. In any case, the toll switching apparatus in the central oillce l0 is controlled, whereby the toll third selector 30 seizes the trunk 001|) extending to the toll line circuit 000 or the trunk 00||n extending to the toll line circuit 000 is seized directly at the toll board 30, assuming that the call is to be routed via the toll line circuit A000 individual to the toll trunk 333 extending betweenI the central oilice |0 and the distant exchange 300. More particularly, either the trunk 000f or 00011. extending to the toll line circuit 000 is seized, whereby the toll linecircuit 000 controls the toll line circuit 500 over the toll trunk 333 and the repeaters 33| and 332 illustrated. More speciiically, when the toll line circuit 000 in the central ofllce |0 is thus seized it operates in order to cause resistance battery potentm to be applied by way or the two line conductors in parallel of the toll trunk 333 and the windings 0|| and 0|3 of therepeating coil 0|0 to-the simplex conductor C0|5. This application of resistance battery potential in the toll line circuit 000 in the central oilice |0 to the simplex conductor C0|5 completes a circuit, including the contacts 5|3, 183 and 115, for energizing the winding of the simplex relay R500 in the toll line circuit 500 in the distant exchange 300, whereby the last-mentioned relay operates. Upon operating, the simplex relay R000 completes, at the contacts 55|, an obvious circuit for energizing the winding of the hold relay R010, 'thereby to cause thelatterrelay to operate.

Upon operating, the hold relay R610 interrupts, at the contacts 61|, a normally completed busy relay R180 to the control conductor C193l of the trunk 190l extending to the incoming selector 3|5 individually associated with the toll l line circuit 500; and completes, at the contacts 612, an obvious path for applying ground potential to the control conductor C193 of the trunk 190, whereby the incoming selector 3|5 is seized preparatory to the reception of a digit to be transmitted over the trunk 190. Also the hold relay R610 completes, at the contacts 611, an obvious path for applying ground potential to the control conductor C506 of thetrunk 50|, thereby to complete obvious multiple circuits for illuminating the signal lamps L|056 etc. disposed at the various positions at the toll board 320 in order to indicate to the operators thereat that the toll line circuit l500 to which the trunk 50| extends and consequently the toll trunk 333 are busy at this time. Further the hold relay R610 completes, at the contacts 613, an obvious circuit, including the contacts 124, and the resistor 691, for energizingthe upper winding of the pulse relay R660, and completes, at the contacts 614 and 615, a circuit, including the resistor 695 and the contacts 115, 183 and 5|3', for energizing the lower winding of the pulse relay R660 via the simplex conductor C4|6. When both the upper and the lower windings of the pulse relay R660 i local battery circuit is without effect at this time. Further the hold relay R610 completes, at the contacts 615, an obvious circuit, including the resistors 693' and 695, for charging the condenser 694, and completes, at the contacts 614, an obvious multiple circuit, including the resistor `693 and the lower winding of the pulse relay R660, for charging the condenser 694.

Upon operating, the pulse relay R660 completes,

at the contacts 66|, an obvious circuit for energizing the winding of the pulse slave relay R120 and an obvious multiple circuit, including the resistor 196, for charging the `condenserl 191, whereby the latter relay operates. Upon operating, the pulse slave relay R120 interrupts, at the contacts 124, the previously traced circuit f for energizingthe upper winding of the pulse ref-v lay R660; however, the latter relay remainsin its operated` position due to the completed hold# ing circuit for energizing the lower winding thereof. Also th'e pulse slave relay R120 completes, at the contacts 122', an obvious circuit for energizing the winding of vthehld relay R1|0, thereby to cause the latter relay to operate. Upon operating, the hold relay R1|0 completes, at the contacts 1I I, an obvious circuit,including the resistor 190, for energizing the upper winding of the select relay R130, thereby to render the latter relay exceedingly fast to operate when the lower winding thereof is subsequently energized, the select relay R130 being of the polarized type. Also the hold relay R1 0 completes, at the contacts 1 3, an obvious multiple circuit for energizing the winding of the hold relay R610. Further the hold relay R1|0 completes, at the contacts -1|2, a loop circuit between the toll line circuit 500 and the incoming selector 3|5 via the trunk 190. 'I'he above-mentioned circuit extends from the line conductor C19| of the trunk 190 by way of the contacts 16|, 12| and 5||, the winding 4|2 of the repeating coil 4 0, the contacts 5 3, the upper winding of the answer relay R140, the lower winding of the select relay R;the contacts 5|5, the winding 4I4 of the repeating coil 4|0, the contacts 5|1, 1|2 and 164 to the line conductor C192 of the trunk i190. When the above-mentioned loop circuit is completed the upper winding of the answer relay'R140 is energized, whereby this relay operates; also the lcwer winding of the select relay R130 is energized, but the latter relay does not operate as it is of the polarized type and thev direction of current ilow in the lower winding thereof is inppposition to the direction of current ilow in the upper winding thereof. Also, upon operating, the hold relay R1|0 cornpletes, at the contacts 1||, a circuit, including the contacts 132, for energizing the winding of the ring relay-R'in order to cause4 the latter relay to operate. Upon operating, the ring relay R150 completes, at the contacts 153, a circuit, including the contacts 132 and 1 and C804, for energizing the Winding of the start relay R820 in the tone detector 800, thereby to cause the latter relay to Uperate.

Upon operating, therstart relay R820 in the l tone detector 800 completes, at the contacts 824. an obvious path for applying ground potential to the start conductor C3|3 ext'ending to the tone detecting unit 8|5, whereby operation of the tone. detecting unit 8|5 is initiated. Also the` start relay R820 completes, at the contacts 82|, an obvious connection between theconductor C80| extending to the toll line circuit 500 and the conductor C8|l extending to the tone detecting unit 8|5, the last-mentioned connection including the condenser 8|8. Further the start relay R820 completes, at the contacts 822, an obvious path for applying ground potential to the conductor C8|2 extending to the tone detecting unit 8|5 and completes, at the contacts 825, an obvious path for applying battery potential by way of the winding of the flash relay R830 to the conductor C8|4 extending to the tone detecting unit 8| 5. Also the start-relay R820 completes, at the contacts 821, a connection including the contacts 856 and 846 between the rotary magnet M812 of the digit switch 810 and the conductor C805 extending to the toll line circuit 500, for a purpose more fully explained hereinafter. When operation of the tone detecting unit 8|5 is thus initiated, ground potential is returned over the conductor C8I4, thereby to complete an obvious circuit, including the contacts 825, for energizing the winding of the flash relay R830, whereby the latter relay operates.

Upon operating, the :tlash lrelay R830 completes,

at the contacts 83|, an obvious circuit for energizing the winding of the control relay R835, thereby to cause the latter relay to operate. Also the ash relay R830 rompletes, at the contacts 833, an obvious path, including the contacts 813, for applying ground potential to the wiper 81| of the digit switch 810, for a purpose more fully.

,tial is' applied to the simplex conductor C4|8 a path, including the contacts 8| 3', 183 and 118, is completed for short-circuiting the winding of the simplex relay R880, thereby to cause the latter relay to restore. Also this application of ground epotential to the simplex conductor C4I8 completes a circuit, including the contacts 8|3', 188,

118, 814 and 818 and the resistor 888. for energizing the lower winding of the pulse relay R880 in the opposite direction, whereby the latter relay restores exceedingly fast in view of the fact that it is oi' the polarized type. At this point it is noted that the above-traced circuit for energizing the lower winding of the pulse relay R880 in the opposite direction includes the resistor 888 having a high resistance value; whereby there is no tendency for the pulse relay R880 to reoperate. Also reoperation of the pulse relay R888 at this time is positively prevented due to interruption of the previously traced circuit for energizing the upper winding thereof. `Upon restoring, the pulse relay R880 interrupts, at the contacts 88|, the previously mentioned circuit for energizing the winding of the pulse slave relay R120 and the previously mentioned multiple circuit for charging the condenser 191, whereby the latter relay restores. Upon restoring, the pulse relay R120 recompletes, at the contacts 124, the previously traced circuit for energizing the upper winding of the pulse relay R880; however, the latter relay does not reoperate at this time as it is of the polarized type. Also when ground potential is applied to the simplex conductor C4l8 the condenser 884 is charged to a slightly higher potential, for a purpose more fully explained hereinafter.

At the conclusion of the first impulse of the digit transmitted over the toll trunk 333, ground potential is removed from and battery potential is reapplied to the simplex conductor C418, thereby to recomplete the previously traced circuit for energizing the winding of the simplex relay R880- and to recomplete the previously traced original multiple circuit for energizing the lower winding of the pulse relay R880, whereby the latter relay reoperates exceedingly fast as it is of the polarized type. as previously noted. Also when battery potential is reapplied to the simplex conductor C4I8 the condenser 894 is discharged partially through the lower winding of the pulse relay R880 in order further to enhance the time response of the latter relay. Upon reoperating, the pulse relay R880 completes, at the contacts 88|, the previously mentioned circuit for energizing the winding of the pulse slave relay R120 and the previously mentioned multiple circuit for charging the condenser 191, whereby the latter relay reoperates. Accordingly, it will be understood that the simplex relay R880 and the pulse relay R888 follow the impulses of the digit transmitted over the toll trunk 888- and consequently over the simplex conductor C418. Also the pulse relay R880 repeats the impulses of the digit mentioned, at the contacts 88|, to the pulse slave relay R128, whereby the latter relay follows the each impulse of the digit, in a manner well un- I derstood.

Also each time the pulse slave relay R120 re stores and then reoperates it completes and then interrupts, at the contacts 128, an obvious circuit,

' including the contacts 1I4, for energizing the winding of the digit relay R840, thereby to cause the latter relay to operate. Further, each time the pulse slave relay R restores and then reoperates it interrupts and then recompletes, at the contacts 122, the previously mentioned cir- -cuit for energizing the winding of the hold relay R1I0. The hold relay R1|0 and the digit relay R are of the slow-to-release type: accordingly, these relays do not restore during impulsing. Moreover, the hold relay R1|0 retains operated the hold relay R810, the latter relay being of the slow-to-release type also. Upon operating, the digit relay R840 completes, at the contacts 84|, an obvious circuit for energizing the winding of the digit slave relay R880, thereby to cause the latter relay to operate. Upon operating, the digit slave relay R850 interrupts, at the contacts 88|, a normally completed path, including the contacts 11| and 81|, the condenser 898 and the resistor 894, across the terminals of the windings `4|2 and 4|4 of the repeating coil 4I0; and interrupts, at the contacts 888, a normally completed connection between the toll line circuit 880 and the conductor C8| l extending to the tone detecting unit 8|8, for a purpose more fully explained hereinafter. Also the digit slave relay R880 completes, at the contacts 882, an impulslng bridge between the line conductors C19| and C182 oi' the trunk 190 short-circuiting the windings 4|2 and 4|4 of the repeating coil 4|0, the lower winding of the select relay R and the upper winding of the answer relay R140. The above-mentioned bridge circuit extends, when completed. from the line conductor C181 of the trunk 180 by way of the contacts 18|, 12|, 882, 1|2 and 184 to the line conductor C182 of the trunk 180. Accordingly, the pulse slave relay R120 repeats the impulses of the digit mentioned, at the contacts 12|, over the trunk 190 to the incoming selector 3| 8, whereby the latter selector is operated in the vertical direction in accordance with the number of impulses of the digit mentioned, in a well-known manner. Further the digit slave relay R880 completes, at the contacts 888. an obvious path for applying ground potential to the conductor C808, thereby to complete a circuit, including the contacts 821, 848 and 888, for energizing the rotary magnet M812 of the digit switch 810 in the tone detector 808, whereby the flatter magnet operates inNy order to drive the wiper 81| of the digit switch 810 one step in the clockwise direction. When the wiper 81| of the digit switch 810 is driven one step in the clockwise direction away from its normal rotary position, the sets of switch springs S814 and S818 are actuated for circuited, as :previously noted; whereby .the answer relay R140 restores.

, At the conclusion of the first digit, battery potential is reapplied in the central oice I to the line conductors ofthe toll trunk 333 and consequently to the simplex conductor C4|6, whereby the -simplex relay R680, the pulse relay R660,

lector 3H. The toll transmission selector 3|| responds to the second digit and seizes a trunk in the designated group extending to one of the the pulse slave relay R120, the hold relay R1l0,

L the hold relay R610, and the ring relay R150 in the toll line circuit 500 in the distant exchange- 300 are retained in their operated positions.- A

Shortly thereafter, the digit' relay R640 restores, thereby to interrupt, at the contacts 64|, the previously mentioned circuit for energizing 'the Winding of the digit slave relay R650, whereby the latter relay restores. Upon restoring, the digit slave groups of toll connectors, such, for example, as the trunk 3|3, extending to. the toll connector A312. The tou ooneotor 3|: responds to the third Accordingly, the Wiper 81| of the digitswitch y .810 occupies its respective rst, second, third relay R650 recompletes, at the contacts 65|the previously traced path for connecting the condenser 595 and the resistor 594 across the terminals of the windings 4| 2 and 4|4 of the `repeating coil 4|0; recompletes, at the contacts 653, the previously'traced connection between the terminal of the winding 4|4 of the repeating coil 4|0 and the conductor C80| extending to thetone detector 800; and interrupts, at the contacts 652, the previously traced bridgevcircvit between the line conductors C19| and C192 Qf the trunk 1 90. Also, upon restoring, the digit slave relay R650 interrupts, at the contacts 656, the previously traced circuit, including the conductor C805, for energizing the rotary magnet M812 of the digt switch 810, whereby the latter magnet restores. When the above-traced bridge circuit between the line conductors C19| and C192 is interrupted, at the contacts 652, incident to the restoration of the digit slave relay R650,l the windings 4|2 and 4| 4 of the repeating coil 4|0, the lower winding of the select relay R130 and the upper winding of the answer relay R140 are again connected in series across the line conductors C19| and C192 and fourth positions at the beginning and, consequently, at the conclusionof the respective first,

of the trunk 100 extending to the incoming sea corresponding group of trunks accessible thereto and then operates automatically in order to select an idle trunk in the previously selected group, all in accordance with conventional practice.

Extension of the call to a substation in the distant exchange Now assuming that the call initiated in the central ofiice I0 and routed via the toll line circuit 400 and the toll trunk 333 to the toll line circuit 500, in the manner described above, is to be extended to a subscriber substation in the distant exchange 300, such, for example, as the substation X, four digits are required. The four digits are transmitted over the toll trunk 333 to the toll line circuit 500 and repeated in the manner explained above over the trunk 190. The

first digit effects operation of the incoming selector 3| 5,-in the manner described above, whereby the incoming selector 3|5 seizes a trunk in the designated group extending to one of the groups of selectors, such, for example, as the trunk 3I0, extending to the toll transmission sesecond, third and fourth digits received by the toll line circuit 500 over the toll trunk 333 from. the central oflce I0.

Also it will be understood that, in the event the incoming selector 3| 5 encounters an alltrunks-busy condition at the conclusion of its operation in response to the first digit, busy tone current will be returned over the trunk 190 in accordance with conventional practice.` In a similar manner, in the event the toll transmission selector3|l encounters an all-trunks-busycondition at the conclusion of its operation in response to the second digit, busy tone current will be returned over the trunk in accordance with conventional practice. Finally, in the event the toll connector 3|2 tests the subscriber line 322 extending to the called substation X as busy` lector 3|5 or by the toll transmission selector 3| I,

busy tone current is returned over the trunk 190, as explained above, at the conclusion of the respective rst or second digit, whereby the busy tone current returned over the trunk is returned over the conductor C80I to the tone detector 800 when the conductor C80| is connected, at the contacts 653, to the terminal of the winding 4|4 of the repeating coil 4|0 incident to the restoration of the digit slave relay R650,v as explained above. At this time the conductor C80| is connected by way of the condenser 8|8 and the contacts 82| to the conductor C8|| extending to the tone detecting unit 8I5, whereby the tone detecting unit 8|5 operates to detect the busy tone current impressed upon the trunk 190. More particularly, the tone detecting unit 8|5 operates in order to cause flashes of ground potential to be returned over the conductor C8|4, whereby the flash relay R830 operates and restores intermittently. At' this time the wiper 81| of the digit switch 810 occupies either its rst or its second position in view of the fact that only the rst digit or only the i'lrst and the second digits have been received vby the toll line circuit 500 over the toll trunk 333 and repeated over the trunk 19,0 to the incoming selector 315 or to the incoming selectorl 3I5 and\the toll transmission selector 3| I.

The first time the* Hash relay R830 restores it interrupts, at the contacts 83|, the previously traced original circuit for energizing the winding of the control relay R835; however, the latter relay remains in its operatedp-osition due to the completed holding circuit for energizing the winding thereof. `Also the iirst time the flash relay R830 restores it interrupts, at the contacts 833, the previously mentioned path for applying ground potential to the wiper 81I of the digit switch 810, .and completes, at the contacts 832, a circuit, including the contacts 831 and 854, for energizing the lower winding of `the control relay R850. When thus energized -the control relay R850 operates to complete, at the contacts 853, an obvious 'holding circuit, including the contacts 826, for energizing the upper winding thereof, and to interrupt, at the contacts 854, the previously traced circuit for energizing the lower winding thereof. Also the control relay R850 interrupts, atthe contacts 852, a point in a circuit traced hereinafter for energizing the Winding of the tone switch relay R840, inter rupts, at the contacts 856, a further point in the previously traced original circuit for energizing the rotary magnet M812, and completes, at the contacts 855, an obvious alternative circuit, including the contacts 831 and 832, for energizing the rotary magnet M812. When thus energized the rotary magnet M812 operates, thereby to drive the wiper 81| vof the digit switch 810 an additional step in the clockwise direction. The first time the flash relay R830 reoperates it interrupts, at the contacts 832, the previously traced alternative circuit for energizing the rotary magnet M812, therebyto cause the latter magnet to restore. 'Also the rst time the ash relay R830 reoperates it completes, at the contacts 833, the

previously mentioned path for applying ground potential to the wiper 81| of the digit switch 810.

In view of the above description oi the mode of operation of the rotary magnet M812 of the digit switch 810 in conjunction with the ash relay R830, it'will be understood that the intermittent operation of the ash relay R830 causes intermittent operation of the rotary magnet M812, whereby the wiper 81| of the digit switch 810 is driven either three or four additional steps in the circuit for energizing the winding of the toneY relay R860. When thus energized the tone relay R860 operates to complete, at the contacts 863, an obvious holding circuit, including the contacts time the supervisory lrelay R110 operates it completes, at the contacts 116, an obvious alternative circuit, including the contacts 583 and the resistor 583, for energizing in multiple the windplying ground pote y ial lby way of the winding of 826, for energizing the winding thereof, interrupts, at the contacts 86 I, the connection between the conductor C803 and the conductor C802, and completes, at the contacts 862, an obvious connection, including the contacts 84|, between the 120 impulse-per-minute conductor C816 and the conductor C803, whereby the supervisory relay R110 operates and restores 120 times Der minute.

Each time the supervisory relay R110 operatesV the simplex relay R 88 to the simplex /conductor C4I6. 'Also each time the supervisory relay R110 restores it recompletes, at the contacts 115, the previously traced original circuit for energizing in multiple the winding of the simplex relay R888 and the lower winding of the pulse relay R660, thereby to retain the latter relays in their operated positions. Accordingly, intermittent operation of the supervisory relay R causes.

alternate ground and battery potentials to be returned over the simplex conductor C4I6 at a rate of complete impulses per minute; which 120 complete-impulses per minute correspond to alltrunksdbusy tone and is returned over the toll trunk 333 to the central omce I0 and consequently overv the calling connection in order to indicate the all-trunks-busy condition mentioned in the distant exchange 300.

Now assuming that no all-trunks-busy condition is encountered either by the incoming selector 3 I 5 or by the toll transmission selector 3| I, no busy tone current is returned over the trunk 190 at the conclusion of the ilrst or second digit. Subsequently, the toll line circuit 500 operates to repeat the third digit over the trunk to the toll connector 3I2, as previously noted, and the wiper 81| of the digit switch 810 in the tone detector 800 is driven to engage the third contact in the associated contact bank. At the conclusion of the thirddigit the rotary magnet M812 restores, thereby to complete, at the contacts 813, the previously mentioned circuit for applying ground potential to the Wiper 81| f the digit switch 810 and conseduently to the engaged third contact in the associated contact bank, whereby a circuit. including the conductor C816 and the contacts 852, is completed for energizing the winding of the tone switch relay R840. When thus energized the. tone switch relay R848 operates to complete, at the contacts 845 a holding circuit. including the contacts 826, for energizing the winding thereof; and interrupts. at the contacts 846. a further point in the previously traced circuit for energizing the rotary magnet M812 of the digit switch 810. Alsoithe tone switch relay R848 completes. at the contacts 843. a circuit. including the contacts 826 and 85| and the set 0i switch springs S814. for energizing the release magnet M813.,whereb.v the latter magnet operates to release the wiper 81| of the digit switch 81u in order to cause tbe wiper noted to be returned tn iis normal rotary position. When the difrit switch 810 is thus released theset of swiich springs S814 is actuated intodi'sengagement, tberehv to interrupt the previously traced circuit for energizing the release magnet M813 in order to cause this latter magnet to restore. rAlso the set of switch springs S815 is actuated into engagement. therebv to cornnlete a circuit. including the con; tacts 844 and 828. for energizing the upper 'winding of the control relay R880. When thus energized the eentrei relay Rm operates to complete, at the contacts 853, a multiple holding circuit, including the contacts 328, for energizing the upper winding thereof. Also the control relay R050 interrupts, at the contacts 85|a further point in the previously traced circuit for energizing the release magnet M813 of the digit switch 810; vinterrupts, at the contacts 830, a further point in the previously traced circuit for energizing the lower winding thereof; and prepares, at the contacts 853, the previously traced alternative circuit for energizing the rotary magnet M312.

The toll line circuit 500 then receives the fourth digit over the toll trunk 333 from the central oilice I and repeats the digit mentioned over the trunk 190 to the toll connector 3|2,.whereby the toll connector 3|2 operates to select the subscriber line 322 extending to tlrecalled substation X, as previously explained. '"At this time the toll connector 3|2 tests the idle or busy condition ofthe subscriber line 322 extending to the called substation X as previously noted; whereupon busy tone current is returned therefrom over the trunk 190 in the event the subscriber line 322 is tested as busy, as previously explained.

Now assuming that the subscriber line 322 ex.- tending to the called substation X is tested as busy by the toll connector 3|2, busy tone current is returned over the trunk 130, as explained above, at the conclusion of the fourth digit, whereby the busy tone current returned over the trunk 190 is detected by the tone detecting unit 8|8 and the ash relay R830 is operated intermittently, all in the manner previously explained.

The intermittentoperation of the flash relay,l

Upon operating, the toney relay R860 completes,

at the contacts 863, the previously traced holding circuit, including the contacts 828, for energizing the winding thereof, and completes, at the contacts 862, an obvious connection, including the contacts 802, between the 60 impulse-per-minuteconductor C3|1 and the conductor C803, whereby a circuit substantially identical to that previously traced is completed for energizing the winding of the supervisory relay R110. 'I'he last-mentioned circuit includes the 60 impulse-per-minute conductor C0|1, whereby the supervisory relay R110 operates and restores at a rate of 60 times per minute.' The operation of the supervisory relay R110 is substantially the xsaine as that previously described. However, in the present example, 60 alternate ground andV battery impulses per minute are returned over the simplex conductor C0|0 and consequently over the toll trunk 333 to the central ofllce l0 and consequently over the calling connection in order to indicate the busy condition mentioned of the subscriber line of thev answer relay R100.

tone detection test atv the conclusion of each digit; whereby the tone detector 800 may discriminate between an all-trunks-busy. condition and a busy condition of a subscriber line extending to a called substation in the distant exchange 300. Further the tone detector 800 selectively controls the toll line circuit 500 in response to the discriminating busy test mentioned, whereby two different types of busy signals respectively corresponding to the two busy conditions mentioned are selectively returned over the toll trunk 333 to the central oilice I0 and consequently to the calling circuit.

Now assuming that the toll connector 3|2 tests the subscriber line 322 extending to the called substation X as idle at the'conclusion of the operation thereof in response to the fourth digit, the toll connector 3|2 controls the toll transmission selector 3| I, whereby the toll transmission selector 3| operates to cause battery potential to be reversed over the loop circuit which now extends between the toll line circuit 300 and the toll 'transmission selector 3||. 'Ihe above-mentioned loop circuit extends between the toll line 3|5 and the trunk 190, as previously explained.

Also this loop circuit includes thelower winding of the select relay F130 and the upper winding Accordingly, the

Vanswer relay R140 occupies its operated position and the select relay R130 operates dueto the reversal of the direction of current flow in the lower winding thereof, the select relay R130 beingofj the polarized type.

Upon operating, the select relay R130 completes, at the contacts 130, an obvious path for short-circuiting the resistor 198, thereby to complete an obvious holding circuit, including the contacts 1|I, for energizing the upper winding thereof. Also the select relay R130 interrupts, at the contacts 132, the-previously traced circuit .for energizing the winding of the ring relay R130 and the previously traced multiple circuitfor energizing the winding of the start relay'R020 in' the tone detector 800; whereby the ring relay R100 restores shortly thereafter, the latter relay being of the slow-to-release type, and the start' relay R020 restores immediately. iAlso theselect relay R130 completes, at the contacts13l, a circuit, including the contacts 1| and 132, for ener-I gizing the winding of the ring relay R100, thereby to cause the latter. relay to operate. Upon restoring, the start .relay R020 in the tone detector 880 completes, the the contacts 023, an obvious alternative circuit, including the set of switch springs S010, for energizing the release magnet l M013, whereby the Klatter magnet operates in order to release the wiper 01| of the digit switch 010` and to cause it to be ret ed to its normal rotary position. When the di it switch 010 is thus re'- leased the set of switch springs S010 is actuated 322 extending to the called substation X in the line circuit 300 over the toll trunk 333 and repeated over the trunk 130 and to make a busy -into disengagement, thereby to interrupt thel previously traced circuit for energizing the release magnet M313, whereby the latter magnet restores. Also, upon restoring, the start relay R820 interrupts, at the contacts 02|. the previou's- 1y traced connection between the conductor C00| andthe conductor C8|| interrupts, at the c ontacts 322 and 820, the previously mentioned pathsfor applying ground potential to the conductora C0|2 and C0|3; and interrupts, at the contacts l 328, the previously traced circuit for energizing.

thewinding of the flash relay R030, thereby to .cause the latter relay to restore. Further the start relay R820 interrupts. at the contacts 626, the previously traced holding circuits for energizing the windings of the control relay R835, the tone switch relay R840 and the control relay R850, thereby to cause the relays mentioned to restore. At this time the tone detector 800 is completely released.

Upon operating, the ring relay R160 completes, at the contacts 163, an obvious holding circuit, including the cont'acts 112, for energizing the lower` winding of the answer relay R140, and interrupts, at the contacts 16| and 164, the previously traced loop circuit 'for energizing in se' 2,367,635 at the contacts 14|, a circuit, including the conv ries the lower winding of the select relay R130 and the upper Winding of the answer relay R140; however, the select relay R130 remains operated due to the completion of the previously traced holding circuit for energizing the upper winding thereof and the answer relay R140 remains operated due to the completion of the previously traced holding circuit for energizing the lower winding thereof. Further the ring relay R160 completes, at the contacts 162 and 165, obvious paths for connecting generator potential by way of the generator conductor C194 and the ballast lamp L195 and ground potential, respectively, to the conductors C19| and C192 of the trunk 190. The application of generator potential and ground potential to the line conductors C19|4 at the contacts 163, the previously mentioned holding circuit forenergizing the lower winding of the answer relay R140, and recompletes, at the contacts 16| and 164, the previously' traced loop circuit, including the trunk 190, for ener-y gizing in series the lower winding of the select relay R130 and the upper winding of the answer relay R140. Also the ring relay R160 interrupts, at the contacts 162 and 165, the previously traced path for projecting generator and ground potentials, respectively, over the line conductors C19| 'and C192 of the trunk 190. The toll connector 3|2 continues to project ringing current over the subscriber line 322 to the called substation X until the subscriber at the called substation X answers the call. At this time the toll connector 3|2 switches through, whereby the projection of. ringing current over the subscriber line 322 to the called substation X is interrupted and the toll transmission selector 3| I is controlled. More particularly, the toll transmission selector 3H is controlled to dry of ground and battery potentials the loop circuit extending between the toll transmission selector 3|| and the toll line circuit 500. When the loop circuit mentioned is thus dried of ground and battery potentials the previously traced circuit for energizing in series the `lower winding of the select relay R130 and the upper winding of the answer relay'R140 is inter.- rupted, whereby the select relay R130 remains in its operated position due to'the completed holding circuit for energizing the upper winding thereof and the answer relay R140 restores. Upon restoring, the answer relay R140 completes,

tacts 1||, 13|, 15| and 86|, for energizing the winding of the supervisory relay'R110,"whereb'y{ the latter relay operates. Upon foperating, the supervisory relay R interrupts, at the contacts? 11|, the previously traced path for connectin'g't'hl resistor 594 and the condenser 595 across the t'i minals of the windings 4|2 and 4|4 of the re-y peating coil 4|0; interrupts, at the contacts'115. the previously traced path for applying ground' potential by way ofthe winding of the simplex relay R680 to the simplex conductor C4l6; and completes, at the contacts 114, the previously traced path for applying battery potential by way of the lower winding of the supervisory relay R6|0 to the simplex conductor C4l6. Also the supervisory relay R110 completes, at the contacts 116, the previously traced alternative holding circuit for energizing in multiple the winding of the simplex relay R680 and the lower winding of the pulse relay R660, thereby to retain the relays mentioned in their operated positions.

The removal of resistance ground potential and the application of resistance battery potential to the simplex conductor C4|6 effect the transmission of answer supervision over the toll trunk 333 to the central oice I0 and the calling circuit. `At this time the calling circuit is connectedby way4 of the apparatus in the central oillcfljtoj the toll'lin'e circuit 400; while thetoll line' circuit 400 is'connected by Way of the repeaters 33| and 332and thetoll trunk 333 to the windings 4| and 4|3 of the repeating coil 4|0; the windings 4|2 and 4|4 of .the repeating coil 4|0 are connected by way of the condenser 4I5, the contacts 5|I, 5|1, 1|2, 12|, 16| and 164, the line conductors C19| and C192 of the trunk 190, the incoming selector 3|5 and the trunk 3|0 to the toll transmission selector 3| and a loop circuit is completed between the called substation X and the toll transmission selector 3| I, including the toll connector 3|2, the trunk 3|3 andthe subscriber line 322. fu'jq'j When the subscriber at the called substationX initiates the release of the established connection, by replacing the receiver of the telephone instrument thereat upon its associated switchhook, in-

terrupting the loop circuit between the called substation X andthe toll transmission selector 3H. the toll transmission selector 3I| operates in order again to supply ground and battery potentials over the previously traced loop circuit, including the trunk 190, wherebynthe lower winding of the select relay R and the upper winding of the' answer relay R140 are again energized in series. When thus energized the answer relay R operates to interrupt, at the contacts 14|, the previously. traced circuit for energizing the. winding of the supervisory relay R110, thereby to cause the latter relay to restore. Upon restoring, the supervisory relay R110 again completes. at the contacts 11 I, the previously traced path for connecting the resistor 594 and the condenser 595 across the terminals of the windings 4|2 and 4|4 of the repeating coil 4|0; and interrupts, at the contacts 114, the previously traced path for ap plying battery potential by way ofthe lower winding of the supervisory relay R6|0 to the simplex conductor C4|6. Also the supervisory relay R110 interrupts, at the contacts 116, the previously traced alternative holding circuit for energizing in multiple the winding of the simplex relay R680 andthe lower Winding of the pulse relay R660; 

